1. Field of the Invention
This invention relates generally to a VTR (Video Tape Recorder), and more particularly is directed to a VTR for recording and/or reproducing a television signal with multiplex audio signals.
2. Description of the Prior Art
A television signal with multiplex audio signals includes a sub-channel signal having a frequency of 31.5 kHz as a sub-carrier and which is frequency-modulated with an audio signal, in addition to a main channel signal which is the same as the sound component of the standard television signal. The television signal with the multiplex audio signals may employ the latter for stereo-phonic or bilingual mode broadcasting.
In the case of stereo-phonic broadcasting, a signal which is the sum of right and left audio signals is transmitted in the main channel and a signal which is the difference therebetween is transmitted in the sub-channel. On receiving such main channel and sub-channel signals, the left and right audio signals are separated therefrom by a matrix circuit. On the contrary, in the case of bilingual broadcasting, a first audio signal is transmitted in the main channel and a second audio signal is transmitted in the sub-channel and these first and second audio signals are respectively derived directly from the received main channel and sub-channel signals. Therefore, on receiving bilingual broadcasting, it is necessary to dispose a switching circuit or the like in order to deliver the first and second audio signals independently, rather than to a matrix circuit, as in the case of receiving stereo-phonic broadcasting.
More specifically, on receiving a television signal with multiplex audio signals, it becomes necessary to determine whether the multiplex audio signals are for stereo-phonic or bilingual broadcasting and to correspondingly change-over the switching circuit to either include or exclude the matrix circuit in the receiving circuit.
To cope with the above, on transmitting the television signal with multiplex audio signals, a control signal of about 55.125 kHz (3.5 fH: fH being the horizontal frequency) which is AM-modulated (Amplitude Modulated) with a frequency of 982.5 Hz for the stereo-phonic mode, or with a frequency of 922.5 Hz for the bilingual mode, is multiplexed on the first and/or second audio signal. On reception of the television signal with multiplex audio signals, its control signal is detected for permitting the above described switching circuit or the like to be changed-over automatically to the required condition.
When recording a television signal with multiplex audio signals on a VTR, in the stereo-phonic mode, the left and right audio signals are obtained separately from each other by means of a matrix circuit and recorded on the tape in respective first and second audio signal tracks and, in the bilingual mode, the first and second audio signals are respectively recorded in the first and second audio signal tracks.
However, in the prior art, the previously described control signal for identifying the stereo-phonic or bilingual mode is not recorded in the audio tracks. For this reason, in case of playback of the signal recorded with the prior art VTR, it is necessary for an operator to manually change-over a switch in response to the content of the reproduced signal and, therefore, a troublesome operation is required to again obtain the broadcast television signal with multiplex audio signals in the stereo-phonic or bilingual mode. Further, in reliance on the content of the video tape, it is quite difficult to decide where to change-over the switch and, moreover, it is always possible that the playback will be started with the switch in the wrong position for the signals recorded on the tape.